/**
 * =========================================================================
 * File        : timer.h
 * Project     : 0 A.D.
 * Description : platform-independent high resolution timer
 * =========================================================================
 */

// license: GPL; see lib/license.txt

#ifndef INCLUDED_TIMER
#define INCLUDED_TIMER

#include "lib/config2.h"	// CONFIG2_TIMER_ALLOW_RDTSC
#if ARCH_X86_X64 && CONFIG2_TIMER_ALLOW_RDTSC
# include "lib/sysdep/arch/x86_x64/x86_x64.h"	// x86_x64_rdtsc
# include "lib/sysdep/os_cpu.h"	// os_cpu_ClockFrequency
#endif

/**
 * timer_Time will subsequently return values relative to the current time.
 **/
LIB_API void timer_LatchStartTime();

/**
 * @return high resolution (> 1 us) timestamp [s].
 **/
LIB_API double timer_Time(void);

/**
 * @return resolution [s] of the timer.
 **/
LIB_API double timer_Resolution(void);


//-----------------------------------------------------------------------------
// scope timing

/// used by TIMER
class ScopeTimer
{
	NONCOPYABLE(ScopeTimer);
public:
	ScopeTimer(const char* description)
		: m_t0(timer_Time()), m_description(description)
	{
	}

	~ScopeTimer()
	{
		double t1 = timer_Time();
		double dt = t1-m_t0;

		// determine scale factor for pretty display
		double scale = 1e6;
		const char* unit = "us";
		if(dt > 1.0)
			scale = 1, unit = "s";
		else if(dt > 1e-3)
			scale = 1e3, unit = "ms";

		debug_printf("TIMER| %s: %g %s\n", m_description, dt*scale, unit);
	}

private:
	double m_t0;
	const char* m_description;
};

/**
 * Measures the time taken to execute code up until end of the current scope; 
 * displays it via debug_printf. Can safely be nested.
 * Useful for measuring time spent in a function or basic block.
 * <description> must remain valid over the lifetime of this object;
 * a string literal is safest.
 * 
 * Example usage:
 * 	void func()
 * 	{
 * 		TIMER("description");
 * 		// code to be measured
 * 	}
 **/
#define TIMER(description) ScopeTimer UID__(description)

/**
 * Measures the time taken to execute code between BEGIN and END markers;
 * displays it via debug_printf. Can safely be nested.
 * Useful for measuring several pieces of code within the same function/block.
 * <description> must remain valid over the lifetime of this object;
 * a string literal is safest.
 * 
 * Caveats:
 * - this wraps the code to be measured in a basic block, so any
 *   variables defined there are invisible to surrounding code.
 * - the description passed to END isn't inspected; you are responsible for
 *   ensuring correct nesting!
 * 
 * Example usage:
 * 	void func2()
 * 	{
 * 		// uninteresting code
 * 		TIMER_BEGIN("description2");
 * 		// code to be measured
 * 		TIMER_END("description2");
 * 		// uninteresting code
 * 	}
 **/
#define TIMER_BEGIN(description) { ScopeTimer UID__(description)
#define TIMER_END(description) }


//-----------------------------------------------------------------------------
// cumulative timer API

// this supplements in-game profiling by providing low-overhead,
// high resolution time accounting of specific areas.

// since TIMER_ACCRUE et al. are called so often, we try to keep
// overhead to an absolute minimum. storing raw tick counts (e.g. CPU cycles
// returned by ia32_rdtsc) instead of absolute time has two benefits:
// - no need to convert from raw->time on every call
//   (instead, it's only done once when displaying the totals)
// - possibly less overhead to querying the time itself
//   (timer_Time may be using slower time sources with ~3us overhead)
//
// however, the cycle count is not necessarily a measure of wall-clock time
// (see http://www.gamedev.net/reference/programming/features/timing).
// therefore, on systems with SpeedStep active, measurements of I/O or other
// non-CPU bound activity may be skewed. this is ok because the timer is
// only used for profiling; just be aware of the issue.
// if this is a problem, disable CONFIG2_TIMER_ALLOW_RDTSC.
// 
// note that overflow isn't an issue either way (63 bit cycle counts
// at 10 GHz cover intervals of 29 years).

#if ARCH_X86_X64 && CONFIG2_TIMER_ALLOW_RDTSC

class TimerUnit
{
public:
	void SetToZero()
	{
		m_ticks = 0;
	}

	void SetFromTimer()
	{
		m_ticks = x86_x64_rdtsc();
	}

	void AddDifference(TimerUnit t0, TimerUnit t1)
	{
		m_ticks += t1.m_ticks - t0.m_ticks;
	}

	void Subtract(TimerUnit t)
	{
		m_ticks -= t.m_ticks;
	}

	std::string ToString() const
	{
		debug_assert(m_ticks >= 0.0);

		// determine scale factor for pretty display
		double scale = 1.0;
		const char* unit = " c";
		if(m_ticks > 10000000000LL)	// 10 Gc
			scale = 1e-9, unit = " Gc";
		else if(m_ticks > 10000000)	// 10 Mc
			scale = 1e-6, unit = " Mc";
		else if(m_ticks > 10000)	// 10 kc
			scale = 1e-3, unit = " kc";

		std::stringstream ss;
		ss << m_ticks*scale;
		ss << unit;
		return ss.str();
	}

	double ToSeconds() const
	{
		return m_ticks / os_cpu_ClockFrequency();
	}

private:
	u64 m_ticks;
};

#else

class TimerUnit
{
public:
	void SetToZero()
	{
		m_seconds = 0.0;
	}

	void SetFromTimer()
	{
		m_seconds = timer_Time();
	}

	void AddDifference(TimerUnit t0, TimerUnit t1)
	{
		m_seconds += t1.m_seconds - t0.m_seconds;
	}

	void Subtract(TimerUnit t)
	{
		m_seconds -= t.m_seconds;
	}

	std::string ToString() const
	{
		debug_assert(m_seconds >= 0.0);

		// determine scale factor for pretty display
		double scale = 1e6;
		const char* unit = " us";
		if(m_seconds > 1.0)
			scale = 1, unit = " s";
		else if(m_seconds > 1e-3)
			scale = 1e3, unit = " ms";

		std::stringstream ss;
		ss << m_seconds*scale;
		ss << unit;
		return ss.str();
	}

	double ToSeconds() const
	{
		return m_seconds;
	}

private:
	double m_seconds;
};

#endif

// opaque - do not access its fields!
// note: must be defined here because clients instantiate them;
// fields cannot be made private due to POD requirement.
struct TimerClient
{
	TimerUnit sum;	// total bill

	// only store a pointer for efficiency.
	const char* description;

	TimerClient* next;

	// how often timer_BillClient was called (helps measure relative
	// performance of something that is done indeterminately often).
	size_t num_calls;
};

/**
 * make the given TimerClient (usually instantiated as static data)
 * ready for use. returns its address for TIMER_ADD_CLIENT's convenience.
 * this client's total (added to by timer_BillClient) will be
 * displayed by timer_DisplayClientTotals.
 * notes:
 * - may be called at any time;
 * - always succeeds (there's no fixed limit);
 * - free() is not needed nor possible.
 * - description must remain valid until exit; a string literal is safest.
 **/
LIB_API TimerClient* timer_AddClient(TimerClient* tc, const char* description);

/**
 * "allocate" a new TimerClient that will keep track of the total time
 * billed to it, along with a description string. These are displayed when
 * timer_DisplayClientTotals is called.
 * Invoke this at file or function scope; a (static) TimerClient pointer of
 * name <id> will be defined, which should be passed to TIMER_ACCRUE.
 **/
#define TIMER_ADD_CLIENT(id)\
	static TimerClient UID__;\
	static TimerClient* id = timer_AddClient(&UID__, #id);

/**
 * bill the difference between t0 and t1 to the client's total.
 **/
LIB_API void timer_BillClient(TimerClient* tc, TimerUnit t0, TimerUnit t1);

/**
 * display all clients' totals; does not reset them.
 * typically called at exit.
 **/
LIB_API void timer_DisplayClientTotals();

/// used by TIMER_ACCRUE
class ScopeTimerAccrue
{
	NONCOPYABLE(ScopeTimerAccrue);
public:
	ScopeTimerAccrue(TimerClient* tc)
		: m_tc(tc)
	{
		m_t0.SetFromTimer();
	}

	~ScopeTimerAccrue()
	{
		TimerUnit t1;
		t1.SetFromTimer();
		timer_BillClient(m_tc, m_t0, t1);
	}

private:
	TimerUnit m_t0;
	TimerClient* m_tc;
};

/**
 * Measure the time taken to execute code up until end of the current scope; 
 * bill it to the given TimerClient object. Can safely be nested.
 * Useful for measuring total time spent in a function or basic block over the
 * entire program.
 * <description> must remain valid over the lifetime of this object;
 * a string literal is safest.
 * 
 * Example usage:
 * 	TIMER_ADD_CLIENT(identifier)
 * 
 * 	void func()
 * 	{
 * 		TIMER_ACCRUE(name_of_pointer_to_client);
 * 		// code to be measured
 * 	}
 * 
 * 	[at exit]
 * 	timer_DisplayClientTotals();
 **/
#define TIMER_ACCRUE(client) ScopeTimerAccrue UID__(client)

#endif	// #ifndef INCLUDED_TIMER